Techniques for producing amides or lactams from corresponding raw material oxime compounds through so-called “Beckmann rearrangement” are industrially very important. The production of these compounds has been performed using a process of allowing fuming sulfuric acid in a stoichiometric amount or more to act upon the raw material, but this process raises an issue of by-production of large amounts of ammonium sulfate to be treated.
To avoid this problem, there has been proposed a process of carrying out a reaction in a polar solvent by using a specific aromatic compound as a Beckmann rearrangement catalyst that places less load on the environment. In this process, the aromatic compound contains at least one carbon atom bound to a leaving group as an atom constituting its aromatic ring, contains a total of at least three atoms selected from heteroatoms and electron-withdrawing-group-containing carbon atoms as atoms constituting the aromatic ring, and two of the three atoms selected from heteroatoms and electron-withdrawing-group-containing carbon atoms are positioned each at the ortho position or para position of the carbon atom bound to the leaving group (see NPL 1 and PTL 1). This process, however, employs a polar solvent in the reaction, and the polar solvent should be removed prior to the separation of a reaction product lactam compound from the catalyst through an extraction operation using an organic solvent and water, because the polar solvent will inhibit the separation. This process is therefore disadvantageous in respect of energy and process from the viewpoint as a process for the industrial production of lactam compounds.